The general objective of this research is to elucidate the mechanisms by which the obligately intracellular parasitic bacteria of the genus Chlamydia penetrate, grow within membrane-limited vacuoles, and avoid natural defenses of host cells in culture. The following specific objectives will be pursued: Phagosomes have been isolated from L cells 2 hours after being infected with C. psittaci. Attempts will be made to isolate the membranes from these phagosomes and to compare their protein content with the membranes from phagosoles which normally fuse with lysosomes. Using radioautographic techniques and electron microscopy, attempts will be made to determine the mechanisms by which the inclusion membrane surrounding chlamydiae increases in surface area in the absence of host protein synthesis. Infection of macrophages with mycobacteria (which multiply within membrane-bound vacuoles which do not fuse with lysosomes) is associated with an increase in cAMP in the macrophages. Attempts will be made to detect adenyl cyclase activity in chlamydiae-containing inclusions using cytochemical techniques. C psittaci, penetrates cells in culture efficiently whereas trachoma organisms do not. The role of parasite-cell and host-cell surface charge in the attachment and subsequent penetration of chlamydiae will be investigated. Attempts will be made to develop a radiochemical assay to detect the fusion of lysosomes with inclusions containing chlamydiae treated in a variety of ways.